The present invention is generally directed to toner compositions, and more specifically to encapsulated toner compositions. In one embodiment, the present invention relates to encapsulated toner compositions comprised of a core comprised of a polymer binder and colorants, including pigments, dyes, or mixtures thereof, and a polymeric shell thereover prepared, for example, by interfacial polymerization. Another embodiment of the present invention relates to shell formation by interfacial polycondensation of a polyisocyanate with a polyol, that is, for example, a carbohydrate having a functionality equal to or greater than that of the polyisocyanate, such as a low molecular weight carbohydrate. The core polymer binder can be generated by the addition polymerization of vinyl monomers after microcapsule shell formation. Specifically, in an embodiment the aforementioned shell forming interfacial polycondensation can be accomplished in the presence of a molar excess of the carbohydrate, or its derivatives. The hydroxylated polyurethane shell thus formed possesses a high degree of hydroxy substitution, and as a result is rendered polar in nature, and is accordingly very effective in containing the relatively nonpolar core polymer binder. Effective containment of core components can be of importance for encapsulated toners since core component leaching could, and in many instances, if not all, causes toner agglomeration and blocking, and the resultant toners would be inferior in performance. These and other disadvantages are eliminated or minimized with the toners of the present invention. In another specific embodiment, the present invention is directed to encapsulated toner compositions which provide high fix images under low pressure fixing conditions, and which toners are comprised of a core of polymer binders and colorants, preferably magnetic pigments such as magnetites, encapsulated thereover by a hydroxylated polyurethane shell derived from the polycondensation of a diisocyanate, a triisocyanate or mixtures thereof with a low molecular weight carbohydrate derivative such as monosaccharides or disaccharides. The fix level of developed image of an encapsulated toner under pressure fixing conditions is generally dependent on the rate of the diffusion of its core components, primarily the core resin, out of the ruptured toner to fix to paper; the fix level accordingly can be considered a function of time, and the optimum fix is usually achieved about several hours to 24 hours after the toner is ruptured. The initial fix, that is the fix level after 1 or 2 minutes of toner rupture, of a number of encapsulated toners at low fixing pressure of, for example, about 2,000 psi is usually from about 5 to 30 percent. This marginal initial fix may not be sufficient with regard to duplex printing since the low initial fix may cause image offset to the pressure roll or severe image smear during the duplex printing process. Accordingly, a specific embodiment of the present invention is to provide encapsulated toner compositions which also offer high initial fix of, for example, in excess of about 40 to about 50 percent, and which toners are obtained by encapsulating a core composition of a polymer binder and a colorant with a hydroxylated polyurethane shell derived from interfacial polycondensation of a polyisocyanate and a monosaccharide or disaccharide, or mixtures thereof, selected from the group consisting of ribose, arabinose, xylose, glucose, gluconolactone, methyl glucopyranoside, mannose, methyl mannopyranoside, galactose, methyl galactopyranoside, sorbose, fructose, maltose, cellobiose, lactose, lactobionic acid and sucrose, and the like. The aforementioned relatively high level of initial fix is believed to be sufficient to overcome the image offset and image smear problems in duplex printing. The aforementioned toners possess a number of advantages as illustrated herein including a high initial fix of developed image to paper of about 40 to about 50 percent within, for example, from about 1 to about 2 minutes after fixing, and a final fix of at least about 85 percent at low fixing pressure of, for example, 2,000 psi in embodiments thereby enabling duplex imaging and printing processes to be properly accomplished; preventing or minimizing leaching or loss of the core components especially the core binder; avoidance or minimization of agglomeration; elimination and/or the minimization of image ghosting; and acceptable powder flow characteristics and surface release properties. In another embodiment of the present invention, the toner compositions obtained can include thereon an electroconductive material thereby permitting compositions with a controlled and stable volume resistivity such as, for example, from about 10.sup.3 to about 10.sup.8 ohm-cm, and preferably from about 10.sup.4 to about 10.sup.7 ohm-cm, which toners are particularly useful for inductive single component development processes. The toner compositions of the present invention also provide a shell with substantially improved mechanical properties, and which shell does not rupture prematurely causing the core component comprised, for example, of a polymer and magnetite, or other pigment to become exposed, and contaminating the image development subsystem surfaces or forming undesirable agglomerates. The toners of the present invention also provide for a complete or substantially complete transfer of toned images to a paper substrate during the development process. The toner compositions of the present invention can be selected for a variety of known reprographic imaging processes including electrophotographic and ionographic processes. In embodiments, the toner compositions of the present invention are selected for pressure fixing processes for ionographic printing wherein dielectric receivers, such as silicon carbide, are utilized, reference U.S. Pat. No. 4,885,220, the disclosure of which is totally incorporated herein by reference. Specifically, the toner compositions of the present invention can be selected for image development in commerical Delphax printers such as the Delphax S9000.TM., S6000.TM., S4500.TM., S3000.TM., and Xerox Corporation printers such as the 4060.TM. and 4075.TM. wherein, for example, transfixing is utilized, that is fixing of the developed image is accomplished by simultaneously transferring and fixing the developed images to a paper substrate with pressure. Another application of the toner compositions of the present invention resides in its use for two component development systems wherein, for example, the image toning and transfer are accomplished electrostatically, and the fixing of the transferred image is achieved by application of pressure with or without the assistance of thermal energy.
The toner compositions of the present invention can, in embodiments, be prepared by a shell forming interfacial polycondensation, followed by an in situ core polymer binder forming free radical polymerization of an addition monomer or monomers initiated by thermal decomposition of a free radical initiator. One embodiment of the present invention is directed to a process for a simple and economical preparation of pressure fixable encapsulated toner compositions by a chemical microencapsulation method involving an interfacial polycondensation and a free radical polymerization, and wherein there are selected, for example, acrylates, methacrylates or styryl derivatives as core monomers, pigments or dyes as colorants, and polyisocyanates and monosaccharides or disaccharides as shell precursors to provide an encapsulated toner with a hydroxylated polyurethane shell. Further, in another process aspect of the present invention the encapsulated toners can be prepared in the absence of flammable organic solvents, thus eliminating explosion hazards associated therewith; and furthermore, these processes do not require the expensive and hazardous solvent separation and recovery steps. Moreover, with the process of the present invention there can be obtained in some instances improved yields of toner products since, for example, the extraneous solvent component can be replaced by liquid shell and core precursors.
The toner compositions of the present invention contain hydroxylated polyurethane shell materials that permit attainment of high fixed images, in particular images with a high initial fix level, while simultaneously enabling effective containment or substantial retention of the core components, thus eliminating or substantially suppressing core binder diffusion and leaching. As a consequence, the problems of toner agglomeration and image ghosting are eliminated or substantially alleviated. Furthermore, the toner compositions of the present invention improve the efficiency of the image transfer process to substrates such as paper in many embodiments. Also, with the toner compositions of the present invention, particularly with respect to their selection for inductive single component development processes, the toner particles contain on their surfaces a uniform and substantially permanently attached electroconductive material thereby imparting certain stable electroconductive characteristics to the particles inclusive of situations wherein these particles are subjected to vigorous agitation. With a number of the prior art toners, the surface conductivity properties of the toner particles may be unstable when subjected to agitation, especially, for example, when electroconductive dry surface additives such as carbon black are selected. Further, with the aforementioned prior art toner compositions there are usually obtained images of low quality with substantial background deposits, particularly after a number of imaging cycles, especially subsequent to vigorous mechanical agitation which results in toner electroconductivity instability as, for example, the additives such as carbon black are not permanently retained on the surface of the toner. Additionally, several of the cold pressure fixing toner compositions of the prior art have other disadvantages in that, for example, these compositions are obtained by processes which utilize flammable organic solvents. The utilization of flammable organic solvents renders the preparative process costly and potentially hazardous since most of these solvents are explosion prone and require costly explosion-proof equipment, and such processes also require expensive solvent separation and recovery steps. Moreover, the inclusion of solvents also decreases the toner throughtput yield per unit volume of reactor size. Furthermore, with many of the prior art processes toners of narrow size dispersity cannot be easily achieved as contrasted with the process of the present invention where narrow particle size distributions are generally obtained. In addition, a number of prior art processes provide deleterious effects on toner particle morphology and bulk density as a result of the removal of solvent and the subsequent collapse or shrinkage of toner particles during the toner work-up and isolation processes resulting in a toner of very low bulk density. These disadvantages are substantially eliminated with the toners and processes of the present invention in some embodiments thereof. More specifically, thus with the encapsulated toners of the present invention control of the toner physical properties of both the core and shell materials can be achieved. Specifically, with the encapsulated toners of the present invention undesirable leaching or loss of core components is avoided or minimized; high initial fix of about 40 to about 50 percent, and a final fix of over 85 percent are obtained; and image ghosting is eliminated in many instances primarily as a result of the use of the polar hydroxylated polyurethane shell. Image ghosting is an undesirable phenomenon commonly encountered in transfix ionographic printing when undesirable toner compositions are utilized. It refers to the repetitious printing of unwarranted images, and arises primarily from the contamination of the dielectric receiver by the unremovable toner materials. This problem can sometimes be partially eliminated by use of suitable surface release agents which aids in the removal of residual toner materials after image transfer. The toner compositions of the present invention eliminate or substantially eliminate the image ghosting problem by providing a microcapsule shell which effectively contains the core binder, inhibiting its leaching, and prevents it from coming into contact with the dielectric receiver during the image transfix process. In addition, the shell materials of the present invention together with the aid of some suitable surface additives also provides excellent surface release properties, thus enabling efficient removal of residual toner materials from the dielectric receiver surface and high image transfer efficiency.
Encapsulated cold pressure fixable toner compositions are known. Cold pressure fixable toners have a number of advantages in comparison to toners that are fused by heat, primarily relating to the utilization of less energy and enabling the use of heatless instant-on imaging apparatus, since the toner compositions selected can be fixed without application of heat. Nevertheless, many of the prior art cold pressure fixable toner compositions suffer from a number of deficiencies. For example, these toner compositions must usually be fixed under high pressure, which has a tendency to severely affect the fixing characteristics of the toner selected. This can result in images of low resolution or definition. High pressure fixing also can result in undesirable paper calendering. Also, with a number of the prior art cold pressure toner compositions substantial image smearing can result from the high pressures used. Many of the prior art cold pressure fixable toner compositions, particularly those prepared by conventional melt blending processes, do not usually provide high image fix levels. Additionally, the cold pressure fixing toner compositions of the prior art have other disadvantages in that, for example, these compositions are generally fixed under high pressure, and provide in some instances, images which are of high gloss and of low crease and rub resistance.
In a patentability search report, the following prior art, all U.S. patents, were recited: U.S. Pat. No. 4,442,194 which discloses encapsulated toners with shells comprised of substances (A) and (B), see column 3 for example, wherein (A) can be an isocyanate and (B) can be an active hydrogen containing compound, see column 4, such as polyols, water, sorbitol, and the like, see column 5; a similar teaching is present in U.S. Pat. No. 4,699,866; U.S. Pat. No. 3,898,171 which discloses an electroscopic powder formulated with sucrose benzoate and a thermoplastic resin, see for example column 2; and U.S. Pat. Nos. 4,465,755 and 4,592,957 as being of possible background interest.
The following U.S. patents located in a patentability search report for encapsulated toners are mentioned: U.S. Pat. No. 3,967,962 which discloses a toner composition comprising a finely divided mixture comprising a colorant and a polymeric material which is a block or graft copolymer, including apparently copolymers of polyurethane and a polyether (column 6), reference for example the Abstract of the Disclosure, and also note the disclosure in columns 2 and 3, 6 and 7, particularly lines 13 and 35; however, it does not appear that encapsulated toners are disclosed in this patent; U.S. Pat. No. 4,565,764 which discloses a microcapsule toner with a colored core material coated successively with a first resin wall and a second resin wall, reference for example the Abstract of the Disclosure and also note columns 2 to 7, and particularly column 7, beginning at line 31, wherein the first wall may comprise polyvinyl alcohol resins known in the art including polyurethanes, polyureas, and the like; U.S. Pat. No. 4,626,490 contains a similar teaching as the '764 patent and more specifically discloses an encapsulated toner comprising a binder of a mixture of a long chain organic compound and an ester of a higher alcohol and a higher carboxylic acid encapsulated within a thin shell, reference the Abstract of the Disclosure, for example, and note specifically examples of shell materials in column 8, beginning at line 64, and continuing on to column 9, line 17, which shells can be comprised, for example, of polyurethanes, polyurea, epoxy resin, polyether resins such as polyphenylene oxide or thioether resin, or mixtures thereof; U.S. Pat. Nos. 4,442,194 and 4,465,755, mentioned herein; and U.S. Patents of background interest include U.S. Pat. No. 4,520,091; 4,590,142; 4,610,945; 4,642,281; 4,740,443 and 4,803,144.
With further specific reference to the prior art, there are disclosed in U.S. Pat. No. 4,307,169, the disclosure of which is totally incorporated herein by reference, microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there are disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes are also selected for the preparation of the toners of this patent. Also, there is disclosed in the prior art encapsulated toner compositions usually containing costly pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,483,912; and 4,397,483.
Interfacial polymerization processes are described in British Patent Publication 1,371,179, the disclosure of which is totally incorporated herein by reference, which publication illustrates a method of microencapsulation based on in situ interfacial condensation polymerization. More specifically, this publication discloses a process which permits the encapsulation of organic pesticides by the hydrolysis of polymethylene polyphenylisocyanate or toluene diisocyanate monomers. Also, the shell-forming reaction disclosed in the aforementioned publication is initiated by heating the mixture to an elevated temperature at which point the isocyanate monomers are hydrolyzed at the interface to form amines, which then react with unhydrolyzed isocyanate monomers to enable the formation of a polyurea microcapsule wall. Moreover, there is disclosed in U.S. Pat. No. 4,407,922, the disclosure of which is totally incorporated herein by reference, interfacial polymerization processes for pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctadecylvinylether-co-maleic anhydride as a soft component.
Furthermore, other prior art, primarily of background interest, includes U.S. Pat. Nos. 4,254,201; 4,465,755 and Japanese Patent Publication 58-100857. The Japanese publication discloses a capsule toner with high mechanical strength, which is comprised of a core material including a display recording material, a binder, and an outer shell, which outer shell is preferably comprised of a polyurea resin. In the '201 patent there are disclosed encapsulated electrostatographic toners wherein the shell material comprises at least one resin selected from polyurethane resins, a polyurea resin, or a polyamide resin. In addition, the '755 patent discloses a pressure fixable toner comprising encapsulated particles containing a curing agent, and wherein the shell is comprised of a polyurethane, a polyurea, or a polythiourethane. Moreover, in the '201 patent there are illustrated pressure sensitive adhesive toners comprised of clustered encapsulated porous particles, which toners are prepared by spray drying an aqueous dispersion of the granules containing an encapsulated material.
Also, there are illustrated in U.S. Pat. No. 4,280,833 encapsulated materials prepared by interfacial polymerization in aqueous herbicidal compositions. More specifically, as indicated in column 4, beginning at line 9, there is disclosed a process for encapsulating the water immiscible material within the shell of the polyurea, a water immiscible organic phase which consists of a water immiscible material, that is the material to be encapsulated, and polymethyl polyphenyl isocyanate is added to the aqueous phase with agitation to form a dispersion of small droplets of the water immiscible phase within the aqueous phase; and thereafter, a polyfunctional amine is added with continuous agitation to the organic aqueous dispersion, reference column 4, lines 15 to 27. Also, note column 5, line 50, wherein the amine selected can be diethylene triamine, and the core material can be any liquid, oil, meltable solid or solvent soluble material, reference column 4, line 30. A similar teaching is present in U.S. Pat. No. 4,417,916.
In U.S. Pat. No. 4,599,271, the disclosure of which is totally incorporated herein by reference, there are illustrated microcapsules obtained by mixing organic materials in water emulsions at reaction parameters that permit the emulsified organic droplets of each emulsion to collide with one another, reference the disclosure in column 4, lines 5 to 35. Examples of polymeric shells are illustrated, for example, in column 5, beginning at line 40, and include isocyanate compounds such as toluene diisocyanate, and polymethylene polyphenyl isocyanates. Further, in column 6, at line 54, it is indicated that the microcapsules disclosed are not limited to use on carbonless copying systems; rather, the film material could comprise other components including xerographic toners, see column 6, line 54.
Other prior art includes U.S. Pat. No. 4,520,091, the disclosure of which is totally incorporated herein by reference, which illustrates an encapsulated toner material wherein the shell can be formed by reacting a compound having an isocyanate with a polyamine, reference column 4, lines 30 to 61, and column 5, line 19; and U.S. Pat. No. 3,900,669 illustrating a pressure sensitive recording sheet comprising a microcapsule with polyurea walls, and wherein polymethylene polyphenyl isocyanate can be reacted with a polyamine to produce the shell, see column 4, line 34.
Illustrated in U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. Further in another copending application U.S. Ser. No. 402,306, the disclosure of which is totally incorporated herein by reference, there are illustrated encapsulated toners with a core comprised of a polymer binder, pigment or dye, and thereover a polymeric shell, which contains a soft and flexible component, permitting, for example, proper packing of shell materials resulting in the formation of a high density shell structure, which can effectively contain the core binder and prevent its loss through diffusion and leaching process. The soft and flexible component in one embodiment is comprised of a polyether function. Specifically, in one embodiment there is disclosed in the aforementioned copending application encapsulated toners comprised of a core containing a polymer binder, pigment or dye particles, and thereover a shell preferably obtained by interfacial polymerization, which shell has incorporated therein a polyether structural moiety. Another specific embodiment of the copending application is directed to encapsulated toners comprised of a core of polymer binder, pigment, dye or mixtures thereof, and a polymeric shell of a polyether-incorporated polymer, such as a poly(ether urea), a poly(ether amide), a poly(ether ester), a poly(ether urethane), mixtures thereof, and the like. With the toner compositions of the present invention, advantages in embodiments thereof include: (1) high fixing, and both high initial and high final image fix levels under low pressure fixing conditions; (2) utilization of a novel class of hydroxylated polyurethane shells derived from polycondensation of low molecular weight carbohydrates and polyisocyanates; (3) the shell materials suppress or inhibit core binder diffusion and leaching process through the incompatibility of the shell and core material; (4) the avoidance in embodiments of the relatively toxic polyamines in the preparation thereof; and (5) in some process embodiments, the effluents from the reaction and post-reaction washings during toner preparation do not require costly special waste treatments since polyamines are not utilized.
Accordingly, there is a need for encapsulated toner compositions with many, and in some embodiments substantially, if not all, the advantages illustrated herein. More specifically, there is a need for encapsulated toners with shells that eliminate or minimize the loss of core components such as the binder resin. Also, there is a need for encapsulated toners wherein images with excellent resolution and superior initial and final image fix can be obtained. Moreover, there is a need for encapsulated toners, including colored toners, wherein image ghosting and smear, toner offsetting, and undersirable leaching of core components and the like are avoided or minimized. Additionally, there is a need for encapsulated toners, including colored toners with, in some instances, excellent surface release characteristics enabling efficient image transfer during image development and fixing processes. Furthermore, there is a need for encapsulated toners which have been surface treated with additives such as carbon blacks, graphite or the like to render them conductive to a volume resistivity level of preferably from about 10.sup.3 to 10.sup.8 ohm-cm, and to enable their use in single component inductive development systems. Moreover, there is a need for pressure fixable encapsulated toners that can be utilized in the transfix development systems under low pressure fixing conditions. There is also a need for processes for the preparation of encapsulated toners with the advantages mentioned herein. Specifically, there is a need for chemical microencapsulation preparative techniques for encapsulated toner compositions, which involve a shell forming interfacial polycondensation process and a core binder forming free radical polymerization process. Furthermore, there is a need for toners and improved processes thereof that will enable the preparation of encapsulated toner compositions whose properties, such as shell strength, core binder molecular weight and the nature of core binder crosslinking, can be desirably controlled.